Republican presidential candidate businessman Herman Cain listens to former U.S. House Speaker Newt Gingrich speak during the CNN GOP National Security debate in Washington, in November. In a recent poll 37 percent of Cain voters picked Gingrich as their back-up.

Herman Cain says he’s trying to figure out whether he should continue his quest for the Republican presidential nomination in light of the latest allegation of inappropriate sexual behavior made against him.

In a conference call with senior staff Tuesday he admitted that Ginger White’s claim of a 13-year affair has created a “firestorm” that might make it difficult for him to campaign, according to a transcript of the call released by the National Review.

Mr. Cain denied Ms. White’s allegation on the conference call. “But if a decision is made, different than to plow ahead, you all will be the first to know,” he told his aides.

The bottom line, according to PPP, is that Cain voters love Mr. Gingrich, and don’t love Mr. Romney.

“If Herman Cain’s support fades to zero in the next few weeks, whether because he drops out or because people abandon him because of all his issues, Newt Gingrich is going to keep on climbing,” concludes a PPP analysis.

There are some interesting numbers within the PPP surveys that complicate this picture, though. Cain supporters in the crucial early caucus state of Iowa were much less likely to list Gingrich as their second choice, for instance. Almost as many (22 percent) said they’d flee to Ms. Bachmann as said they’d go for Gingrich (24 percent).

Is it possible a Cain collapse would resurrect Bachmann’s Iowa chances? She was born there, and won the Ames, Iowa, straw poll, after all. Stranger things have happened already this campaign cycle. Remember when Gingrich’s campaign looked like it might be the worst ever for a major presidential contender?

Anyway, the conventional wisdom at the moment is that Romney would love Cain to hang in there, since he (Cain) would siphon away voters from other anti-Romney candidates, which is to say, all the rest of them.

Romney may need a peloton behind him if he’s going to maintain his front-runner status. He just can’t seem to get up over the hump of 30 percent of GOP voters nationwide.

The tenor of the Romney campaign might change if that does happen. Right now the Mittster is running as if he’s already won the nomination. He spends most of his time directing attacks at President Obama.

But if an avalanche of Cain voters bumps Gingrich up to 35 percent or so, Romney may have little choice but to turn more direct fire on the ex-Speaker of the House.